The study of the natural history of periodontal disease in Sri Lankan tea laborers and Norwegian males is continuing. Future studies include (1) completing the analysis of the longitudinal impact of dental restoration in a gingival location and their relationship to the initiation and progression of periodontal disease. Also, (2) the study of gingival recession in a population who practiced mechanical oral hygiene daily and in a population where oral hygiene never was practiced will be finished and submitted for publication. (3) Stability of the gingival lesion and conversion of gingivitis to periodontitis are the critical issues in the quantitative destruction of the periodontium and can only be studied with some precision in longitudinal materials. These studies will be based on data from both populations. (4) Bacteriological and immunological studies of the two populations are also underway. The specific aims of these studies are to relate the presence and absence of selected periodontal pathogens and peripheral blood antibody titers to the rate of periodontal destruction in the two groups. (5) Studies of the pattern and rates of tooth loss over the twenty-year period in the Sri Lankan tea laborers will be initiated. (6) The problems of method errors and reproducibility in periodontal epidemiology which were studied during the previous period will be completed and the results published. The two master data sets in SAS for the longitudinal surveys in Norway 1969-1988 are: LOE.NOR.AVO (All Valid Observations) and LOE.NOR.IAS (In All Surveys) are completed, for Sri Lanka 1970-1990: LOE.SRIL.AVO (All Valid Observations) and LOE.SRIL.IAS (In All Surveys).